1. Field of Invention
The present invention relates to an improved sideframe in a wheel-truck assembly for supporting a railcar, the sideframe having a bolster window opening that accommodates various truck suspension designs.
2. Description of Related Art
The opposed ends of a railcar body are commonly supported on spaced-apart wheel-truck assemblies for travel along a railway track. A standard railcar wheel-truck assembly generally has a laterally spaced pair of sideframes which are longitudinally operable along the tracks and parallel to the longitudinal axis of the railcar. The sideframes are positioned parallel to the direction of travel of the wheels and to the rails. A bolster, which is transversely positioned to the longitudinal direction of the railcar, couples the sideframes and has the car body supported on bolster center plate sections.
Each sideframe is usually a single casting comprised of an elongated member which has pedestal jaws on each end. The jaws are adapted to receive wheel axles which extend transversely between the spaced sideframes. A bolster opening, or window, formed in the sideframe receives the truck bolster. The bolster is typically constructed as single cast steel section and each end of the bolster extends into each of the sideframe bolster openings. Each end of the bolster is then supported by a spring group that rests on a horizontal extension plate projecting from the bottom of the bolster opening.
The bolster opening, or window, and the spring groups supporting the bolster, allow bolster movement relative to the sideframe. Movement of the bolster relevant to the sideframe may be caused by, for example, railway track conditions, movement of the car body, and the like.
Railway track conditions can include rail running surface variations or discontinuities from differential settling of track on its ballast, rail wear, corrugations, rail misalignment, worn switch frogs or misaligned switch points, as well as the intersection of rails for flange clearance, switches where switching points match with running rails, and rail joints. During normal railcar usage or operation, these and other variations can result in wheel-truck oscillations, which may induce the railcar body to bounce, sway, rock or engage in other unacceptable motions. Wheel-truck movements transferred through the suspension system may reinforce and amplify the uncontrolled motions of the railcar from track variations, which action may result in wheel-truck unloading, and a wheel or wheels of the truck may lift from the track.
The Association of American Railroads (AAR) establishes the criteria for railcar stability, wheel loading and spring group structure. These criteria are set or defined in recognition that railcar body dynamic modes of vibration, such as rocking of sufficient magnitude, may compress individual springs of the spring group at alternate ends of the bolster, even to a solid or near-solid condition. This alternate-end spring compression is followed by an expansion of the springs, which action-reaction can amplify and exaggerate the “apparent” wheel loading on the suspension system and subsequent rocking motion of the railcar, as opposed to the actual or “average” weight or load from the railcar and therein. As a consequence of the amplified rocking motion, and at large amplitudes of such rocking motion, the contact force between the rails and the wheels can be dramatically reduced on the alternate lateral sides of the railcar. In an extreme case, the wheels can elevate and misalign from the track, which enhances the opportunity for a derailment.
There are various modes of motion of a railcar body, that is bounce, pitch, yaw, and lateral oscillation, and roll. In car body roll, or twist and roll as defined by the AAR, the car body appears to be alternately rotating in the direction of either lateral side and about a longitudinal axis of the railcar. Car body pitch can be considered a forward to rearward rotational motion about a transverse railcar axis of rotation, such that the railcar may appear to be lunging between its forward and reverse longitudinal directions. Car body bounce refers to a vertical and linear motion of the railcar. Yaw is considered a rotational motion about a vertical axis extending through the railcar, which gives the appearance of the car ends moving to and fro as the railcar moves down a track. Finally, lateral stability is considered an oscillating lateral translation of the car body. Alternatively, truck hunting refers to a parallelogramming or warping of the railcar truck, not the railcar body, which is a separate phenomena distinct from the railcar body motions noted above. All of these motion modes are undesirable and can lead to unacceptable railcar performance, as well as contributing to unsafe operation of the railcar.
The spring group arrangements support the railcar and damp the relative interaction between the bolster and sideframe. Each spring group typically includes a plurality of coil springs extending between a sideframe spring seat portion (i.e., bottom of the bolster opening) and an undersurface of the bolster end spaced above the respective sideframe spring-seat. There have been numerous types of spring groups utilized for railcar suspension systems, such as concentric springs within the spring group; five, seven and nine spring arrangements; elongated springs (for use with a friction shoe); and, short spring-long spring combinations (for use with a friction shoe) within the multi-spring set. These are just a few of the many noted spring arrangements that have been positioned between sideframe and bolster end assemblies. These spring assemblies must conform to standards set by the AAR, which prescribes a fixed spring height for each coil spring at the fully-compressed or solid spring condition. The particular spring arrangement for any railcar is dependent upon the physical structure of the railcar, its rated weight-carrying capacity and the structure of the wheel-truck assembly. That is, the spring group arrangement must be responsive to variations in the track as well as in the railcar such as the empty railcar weight, the laden-to-capacity railcar weight, railcar weight distribution, railcar operating characteristics, available vertical space between the sideframe spring-platform and the bolster end, the specific friction shoe design and, other operating and physical parameters. Accordingly, different spring group arrangements may be required for different railcar designs and/or operating conditions including empty railcar weight, railcar size, railcar weight distribution and the like.
In addition to the spring group arrangements, a friction shoe assembly may be utilized to help control the dynamic responses of railcar trucks by providing bolster-to-sideframe damping. Friction shoes include a friction wedge in a bolster pocket (an opening in the bolster end coupling the sideframe), which wedge is biased to maintain frictional engagement with the sideframe. Friction shoes dissipate suspension system energy by frictionally damping relative motion between the bolster and sideframe.
Winged friction shoes are most generally utilized with the friction shoe wings contacting complementary inner surfaces of the bolster pockets. A retention or control spring, which biases the friction shoe and maintains it against the bolster pocket surface and the sideframe column wear surface, is supported by the horizontal extension plate, or spring seat, of the sideframe bolster opening beneath the friction shoe.
Generally, different spring group arrangements and, if necessary, friction shoe assemblies require different sideframe structures with differently sized bolster windows therein that accommodate the different spring group arrangements and friction shoe assemblies. For example, one sideframe designed and manufactured by ASF-Keystone, has column wear plates with a 0.375 inch thickness, a 9.44 inch length and a 8.5 inch width. Another sideframe designed by Standard Car Truck Company and manufactured by ASF-Keystone has a 0.5 inch thick column wear plate, a 10.0 inch length and a 10.0 inch width. Yet another sideframe has a 0.5 inch thick column wear plate, a 9.44 inch length and a 7.5 inch width.
Because different spring group arrangements and different shoe assemblies require different sideframe structures with different sized bolster windows therein, additional maintenance, tooling, and increased inventory is required to maintain the various sideframes and suspension systems. Specifically, a spring group arrangement with its corresponding bolster window, when in use, may require maintenance. Springs may need to be replaced and/or repairs may need to be made to the spring group arrangement, shoe, and/or bolster opening. Specific tooling is required for the sideframes, spring group assemblies, friction shoe assemblies, and the like. Each time a decision is made as to which parts to replace and/or repair, a potential for errors increases. Further, an increased inventory must be maintained so that the required parts are readily accessible. Accordingly, a multi-purpose universal sideframe with a bolster opening that can accommodate various spring group arrangements and friction shoe assemblies would decrease needed tooling and inventory.